Silicon micromachining has developed over the last decade as a means for accurately fabricating small structures without requiring assembly of discrete components. Such processing generally involves the selective etching of a silicon substrate and depositions of thin film layers of semiconductor materials. Silicon micromachining has recently been applied to the fabrication of both rotary and linear microactuators which exhibit planar geometries and gap separations on the order of 1-2 microns and lateral dimensions on the order of 100 microns or more.
The small sizes of such microactuators and the characteristics of silicon micromachining combine to produce electro-mechanical characteristics significantly different from those of conventional devices. Electrostatic forces are generally found to be larger than the magnetic alternatives for devices scaled to micro-dimensions. Electrostatic micromotors have a number of advantages over magnetic micromotors or actuators. Static excitation of a magnetic motor requires static currents through its windings, leading to persistent conduction losses. Static excitation of electrostatic motors requires static voltages across gaps, which can be sustained with little loss. An electrostatic motor thus has inherently less losses than a magnetic motor at standstill. This relationship also holds as an electrostatic actuator increases in speed. Electrostatic actuators also avoid the need for magnetizable materials which exhibit eddy current and hysteresis losses.
Recent reports relate the fabrication of a micromotor which includes a rotor and laterally positioned electrostatic stators. Others have also reported on the construction of linear-electrostatic actuators (i.e., see Fujita et al., in "The Principle of Electrostatic Linear Actuator Manufactured Silicon Micromachining", Proceedings of the Fourth Conference on Solid-State Sensors and Actuators, Tokyo, Japan, pages 861-864, 1987 and "Electrostatic Actuators For Micromechatronics", Proceedings of the IEEE MicroRobots and Teleoperators Workshop, 1987. Fujita et al. describe an actuator which includes a plane wafer having embedded strip electrodes and a cylindrical roller extending thereover and aligned therewith. The strip electrodes on one side of the roller are activated by an electric field which tends to attract the roller and make it rotate. As the roller passes over a strip electrode, the electrode is discharged and another in the forward direction is charged to maintain the movement.
A further electrostatic actuator, which is applied to the switching of optical fibers is described by Jebens et al., in "Microactuators For Aligning Optical Fibers" Sensors and Actuators, Vol. 20, pp. 65-73, 1989. In the Jebens et al. actuator, electric fields are used to move a fiber between Vee groove stops. The structure comprises upper and lower plates with Vee grooves, a fiber or fibers, a bias spring and appropriate electrostatic voltage sources. An applied voltage causes a fiber to move into contact with one Vee groove and to remain there so long as the voltage is applied.
It is an object of this invention to provide an improved electrostatic microactuator.
It is another object of this invention to provide an improved electrostatic microactuator which exhibits a plurality of actuating positions that are stable, even in the event of a loss of power.
It is still another object of this invention to provide an electrostatic microactuator that is susceptible to construction in silicon-based technology.